New detector weighs in: neutrinos don’t exceed light speed

We now have yet another indication that neutrinos cannot travel faster than the speed of light after all, provided by a neighbor of the OPERA detector that set off the fuss in the first place. OPERA's detector sits deep underground at Gran Sasso in Italy, where it receives neutrinos from a beam generated at CERN, 730km away on the French-Swiss border. Because the neutrino beam spreads out over the intervening distance, it's possible to run multiple detectors at the same site, all listening in on the same beam. The team running one of Gran Sasso's other detectors (called ICARUS) has now performed time-of-flight measurements on neutrinos and determined that they don't seem to be moving faster than light.

These results are significant because they largely took advantage of precisely the same infrastructure used to generate the OPERA results. ICARUS used the short, widely spaced bunches of neutrinos produced by CERN to help narrow down potential errors in the earlier results (read our discussion of these errors). The ICARUS team also used the same timing and position infrastructure used by OPERA, which gives them uncertainties of only nanoseconds and centimeters, respectively. WIth all that in place, the ICARUS team captured data from the arrival of seven neutrinos.

With just about everything but the detector itself identical between the two tests, the ICARUS team concluded, "The result is compatible with the simultaneous arrival of all events with equal speed, the one of light." (Neutrinos have such a small mass that it's relatively easy to accelerate them to a speed that is only marginally slower than light.)

One difference between the two detectors is the technology used to detect the arrival of neutrinos—OPERA uses a photographic emulsion, while ICARUS uses liquid argon. It's possible that this difference may provide an indication of why the results differed.